1. Field of the Invention
This invention relates generally to jet pump stabilization in nuclear reactors and, more particularly, to an auxiliary wedge apparatus, for modifying jet pump wedge positioning assemblies within a nuclear reactor pressure vessel.
2. Description of Related Art
As detailed by Wivagg in U.S. Pat. No. 7,023,949 (“Wivagg '949”). Boiling water reactors (“BWRs”) are designed to generate steam in reactor pressure vessels (“RPVs”) by heating the water surrounding uranium-containing tubes of fuel assemblies located in the RPV core regions. The RPVs have recirculation loops designed to facilitate the circulation of water in the core regions. The recirculation loops pump water out of the RPVs and return the water to the inlets of jet pump assemblies located in annular regions in the RPVs surrounding the core regions. The jet pump assemblies are designed to entrain the surrounding water in the annular regions and then discharge the water in a manner that induces a desired flow pattern in the core regions. The jet pump assemblies are subject to vibrations caused by hydraulic forces due to the flow of water. Thus, in one BWR design, the jet pump assemblies are horizontally supported against vibration within brackets by a suspension system including a wedge movably mounted on a vertically oriented guide rod that is attached to a jet pump assembly. The wedge, which may weigh about seven pounds, is designed to slide downwardly under the force of gravity into the space between the bracket and the jet pump assembly and thereby urge the jet pump against adjustment screws.
This design is shown in prior art FIGS. 1-3 (from Wivagg '949), wherein, in FIG. 1, nuclear reactor 10 contains outside reactor pressure vessel 12, interior core shroud 18, surrounding reactor core assemblies 20, including fuel, usually UO2 contained in zirconium based tubes, not shown. The core assemblies generate steam from cooling water. Inlet feed water 22 passes into recirculation water outlet nozzle 33 and is pumped to water inlet nozzle 42 via pumping loop (not shown) and passes to riser piping 44.
Riser piping 44 terminates at a manifold 48, sometimes referred to as a “ramshead.” Each jet pump assembly 46 of the pair generally includes an inlet 50 adjacent the manifold 48 that is open to an annular region defined by the wall of the RPV pressure vessel 12 and wall of the core shroud 18 for entraining the surrounding water in the annular region, a mixing section 52 and a diffuser section 54 supported on a crossplate 56. The jet pump assembly 46 may have a boss 49 on its periphery surface as shown in FIG. 2. In the prior art, each jet pump assembly 46 had an associated main wedge 60 that was movably mounted on a vertically extending guide rod 62 fastened to the jet pump assembly 46. As shown in prior art FIG. 2, the main wedge 60 was designed to slide vertically through an opening 68, better shown in FIG. 3, in a restrainer bracket 70, having adjustment set screws 80, therethrough to contact the jet pump assembly 46. The bracket 70 was attached to the riser pump piping 44 by welds 72 or other suitable means. As shown, there are no wedges near the adjustment set screws 80 of FIGS. 2 and 3. The weight of the main wedge 60 provides a sufficient force urging the jet pump assembly 46 against two (or more) adjustment set screws 80 for horizontally supporting the jet pump assembly 46 against hydraulic forces and vibrations. The outer surface of the main wedge 60 could be inclined relative to the edge surface of the bracket 70.
Erbes et al. (U.S. Pat. No. 6,052,425) in their FIG. 2 show a plurality of set screws 32A to D passing through restrainer brackets 28A and B. The main wedges are shown as 30A and B disposed away from the set screws. This provides only two restraining wedge assemblies on opposite sides of inlet mixers assemblies 16A and B. U.S. Pat. No. 7,627,074 (Erbes et al.) teaches dual spring wedges contained within a U-shaped bracket where dual guide rods pass through the top of the U-shaped bracket, through the springs to contact dual wedges. Problems associated with this design are complexity and probable cost. Other patents dealing with jet pump wedges include U.S. Pat. Nos. 4,675,149; 6,320,923; 6,490,331; and 6,788,756 (Perry et al.; Wivagg et al.; Erbes; and Erbes, respectively). Existing designs usually require that the space between the mixer belly band and the restrainer bracket that is being occupied, needs to be measured and therefore the wedge assembly needs to be machined to fit each specific location.
What is needed is a simplified wedge design that does not need to be machined at site and does not require the removal of jet pumps for installation greatly reduces the cost of implementing the repair and is a significant advantage to the owner. What is also needed is an auxiliary wedge assembly disposed next to, over, or in some connection with the set screws and secondary bracing means.
It is therefore an object of this invention to provide a design that installs from above without removing jet pump hardware and provides a mechanism to accommodate a large range in manufacturing variation in jet pump positioning.